Federal health officials on Monday approved the first generic versions of the blockbuster drug Zyprexa, an expensive treatment for schizophrenia and bipolar mood disorder.

Zyprexa posted sales of $5.7 billion last year for Indianapolis-based drugmaker Eli Lilly and Co Inc., according to prescription tracking company IMS Health. Lilly's patent protection on the drug ended Monday.

The new low-cost versions of the drug will be marketed by Indian generic drugmaker Dr. Reddy's Laboratories and by Teva Pharmaceutical Industries, based in Israel.

Zyprexa is part of a class of medications called atypical antipsychotics that effect levels of dopamine, a brain chemical that controls behavior, mood and movement. Doctors overwhelmingly embraced the drugs in the 1990s over older treatments, because they were thought to be less likely to cause side effects like muscle tremors and spasms. The newer medications have their own side effects; including weight gain, high blood sugar and drowsiness.

Drugs like Zyprexa can cost up to $500 per month. Generic versions can cut the cost by up to 80 percent.

The Food and Drug Administration approves generic versions of medications after the patent on the original drug expires or has been ruled invalid in court.

Lilly also faces the loss of revenue from its No. 2-selling drug, the antidepressant Cymbalta, in 2013. Cymbalta is on pace this year for $4 billion in sales.